A MAC Protocol Research Based On Neighbor Beam Alignment And Tracking For Mobile Ad Hoc Networks With Directional Antennas

Directional wireless ad hoc networks, which have the advantages of single hop and single hop transmission, high space division multiplexing rate and network throughput, have received extensive attention from researchers. In this paper we focus on the directional mobile Ad Hoc network medium access control protocol and propose the overall design scheme of the Neighbor Beam Alignment and Tracking MAC Protocol(AT-MAC). The protocol is based on the whole network synchronization, the time axis is divided into continuous equal frame, and each frame is divided into three stages: neighbor discovery, neighbor tracking and data transmission. The neighbor discovery phase uses the RBTH-ND mechanism to found neighbors, and based on random reservation mechanism to agree the tracking slot number; Neighbor tracking stage uses antenna DOA function and LD-NT mechanism to periodiclly tracking the neighbor nodes that have been discovered and order the data transmission sub slots; The data transfer phase is used to transmit data packets between neighbor nodes. In the framework of the overall design scheme, the main innovative achievements of this paper include:(1) According to the particularity of the directional antenna "deaf", puts forward the Random Backoff and Three-way Handshake Based Neighbor Discovery Mechanism. The mechanism uses Markov chain to modeling the random backoff mechanism of beam alignment request frame in the process, obtained the expressions for the steady-state probability, and then combined with the computational geometry method to obtain the expression of beam scanning alignment probability. Numerical simulation and analysis results show that the proposed mechanism can effectively improve the efficiency of neighbor discovery under directional conditions compared with the existing typical neighbor discovery mechanism. Based on the above model, the parameters which affect the neighbor discovery probability are analyzed and discussed, which provide the basis for the parameter setting of neighbor discovery mechanism in AT-MAC protocol.(2) Aiming at the node mobility characteristics, using the DOA function of the antenna, a neighbor tracking mechanism based on link duration prediction is proposed. The mechanism determines and updates the location of the neighbor nodes by periodically tracking the packet. Tracking cycle is an important parameter that affects the performance of neighbor tracking efficiency and network throughput.This mechanism establish a two-dimensional planar node motion model, on the basis of the relative rate of probability density between nodes and the distance between nodes and the relative movement direction of node to determine the distribution function of current link duration. The simulation results prove the correctness of the motion model and the link duration distribution function. Further to analyze the link duration distribution function of the numerical results, it conclud the relationship between tracking cycle and the efficiency of tracking and data transmission efficiency, provides the basis for AT-MAC protocol neighbor tracking parameter settings.On the basis of the above conclusions, the paper presents the simulation and performance analysis of the AT-MAC protocol in the network simulation environment. Firstly, the frame length range of the optimal saturation throughput can be obtained under the condition of different network nodes. Secondly, according to the different network load, the number of network nodes and the number of traffic flow, AT-MAC protocol are compared with the existing protocol on the network performance. Simulation results are proved that in the network traffic load and business flow number tends to saturation, AT-MAC protocol is proposed in this paper can achieve higher throughput compared with the existing similar protocol, and the advantages of AT-MAC protocol are more prominent in the number of neighbor nodes.